In the fabrication process of a semiconductor device, it is indispensable to perform a hydrogen sintering process which performs thermal processing on a substrate for an electronic device on which substrate various semiconductor devices are formed in a hydrogen atmosphere. By performing such a hydrogen sintering process, in a MOSFET (Metal-Oxide-Semiconductor Field Effect Transistor), for example, dangling bonds at the interface region between a channel substrate and a gate insulation film are terminated with hydrogen radicals, and degradation of the electric properties of the semiconductor devices caused by capturing of electric charges by the dangling bonds is suppressed.
There are various semiconductor devices that use a hydrogen sintering process. Specific examples of such semiconductor devices are: a logical device that requires a high-speed operation; a memory device represented by DRAM using a high dielectric constant material (High-k) as an interelectrode insulating film; and a TFT (Thin Film Transistor) formed on a glass substrate. A description is given below of the reason the semiconductor devices require a hydrogen sintering process.
On the other hand, a high dielectric constant material (High-k) such as Ta2O5 is used as an interelectrode insulating film used for a memory cell of DRAM. However, when a semiconductor device including such a high dielectric constant material is processed (e.g., etching or a hydrogen sintering process) under a condition where a large quantity of hydrogen radicals exist, degradation of characteristics such as an increase in leakage current and a reduction of dielectric constant tend to occur (refer to Atsuhiro Tsukune, “Cu Damascene Formation Process”, The 8th semiconductor process symposium, Sep. 20, 1999, pp. 71–79).
In addition, since a TFT is formed on a glass substrate, it is essential to perform a process at low temperature of 400° C. or less. However, it is difficult to form an oxide film having good characteristics in such a temperature region by thermal oxidation. Thus, at present, an oxide film formed by CVD or plasma oxidation is used as a gate insulation film. However, the insulating property of the oxide film fabricated by such methods is significantly inferior to that of a thermal oxide film, and a problem of an increase in energy consumption due to an increase of leakage current occurs, which is disadvantageous for application to a mobile terminal requiring low electric power consumption (refer to N. Sano, M. Sekiya, M. Hara, A. Kohno and T. Sameshima, “Improvement of SiO2/Si interface by low-temperature annealing in wet atmosphere”, Applied Physics Letters, volume 66, Number 16, 1995, pp. 2107–2109).
In order to improve the characteristics of such a gate insulation film, a hydrogen sintering process by thermal processing has been used. However, when forming hydrogen radicals by heat treating, high temperature of 450° C. or more is required. Hence, application to a SiGe substrate and a TFT, which require low temperature processing, is difficult. Additionally, in a case where a hydrogen sintering process by thermal processing is used, hydrogen radicals are mainly controlled by temperature. However, in formation of a semiconductor device in which a heat-resistant material (a material having high heat stability) and a material easily affected by heat (a material having low heat stability) are mixed, it is difficult to establish an optimum process. Further, though High-k materials used as an interelectrode insulation film of a DRAM are promising for the next generation gate insulation film, the materials have a problem of, for example, an increase in the thickness of an oxide film due to crystallization or reaction to silicon when subjected to a high-temperature process after formation of the film. Hence, it is anticipated that it will be difficult to use a hydrogen sintering process using heat on a semiconductor device mounting thereon a High-k gate insulating film.
Wet annealing, which perform annealing in a H2O atmosphere of about 300° C., has been proposed as a process covering the above-mentioned shortcomings (Sano et al., op cit., and D. Tchikatilov, Y. F. Yang and E. S. Yang, Appl. Phys. Lett. 69 (17) 21 Oct. 1996). However, since the time period of annealing is about three hours, which is a long time, it seems that using wet annealing for mass production is difficult.
Therefore, a method using plasma, which can easily form and control hydrogen radicals at a low temperature of 400° C., is drawing attention as a most promising method for forming hydrogen radicals. There have already been reported a large number of hydrogen radical formations using plasma. However, these plasma processes are techniques developed with the aim of cleaning (Y. Aoki, S. Aoyama, H. Uetake, K. Morizuka and T. Ohmi, “In situ substrate surface cleaning by low-energy ion bombardment for high quality film formation”, J. Vac. Sci. Technol. A11(2), March/April 1993, pp. 307–313), and have problems of, for example, plasma damage due to high electron temperature and difficulty in increasing the area processed.
On the other hand, recently, there has been proposed a plasma formation method, which uses a planar antenna and microwaves, as a plasma processing method intended to form a gate insulation film.
In the method, a noble gas of, for example, He, Ne, Ar, Kr and Xe is supplied together with a gas including oxygen or nitrogen via a ring shower plate provided above a substrate to be processed to the space between the substrate to be processes and the shower plate. By emitting microwaves from behind a planar antenna member (slot plane antenna; SPA) provided above the shower plate, the microwaves are propagated via the antenna. A technique has been proposed in which a noble gas is plasma-excited in the above-mentioned space by using the microwaves, and at the same time, radicals of a gas including oxygen or a gas including nitrogen, for example, oxygen radicals O* or nitrogen radicals N*, are formed, thereby oxidizing or nitriding a surface of a silicon substrate.
Since the electron density of the plasma formed by this method is high, a large volume of radicals is formed even at a low substrate processing temperature. In addition, since the electron temperature is low, plasma damage, which becomes a problem in other plasma formation methods, is low. Further, since the microwaves propagated via the planar antenna uniformly form plasma in a large area, it is reported that good application is obtained with respect to a substrate having a large area such as a wafer having a diameter of 300 mm and a TFT display apparatus substrate (Katsuyuki Sekine, Yuji Saito, Masaki Hirayama and Tadahiro Ohmi, J. Vac. Sci. Technol. A17(5), September/October 1999, pp. 3129–3133).
With the use of such a technique, it is possible to directly perform an oxidizing or nitriding process on a surface of a substrate for electronic devices even at a low substrate temperature of 400° C. or less.